The AVS Melting Process is a method for vitrifying waste, such as nuclear waste, in a disposable canister. The waste may be combined with additives promoting the creation of a vitrified product. Whether the waste is untreated or combined with additives, it is referred to hereinafter as xe2x80x9cwaste.xe2x80x9d
The disclosure of U.S. patent application Ser. No. 09/850,623 filed May 7, 2001 is incorporated herein by reference. The disclosure of U.S. Pat. No. 5,678,237, which describes a canister and related method of in-situ vitrification of waste materials in a disposable canister, is incorporated herein by reference.
The terms xe2x80x9ccanisterxe2x80x9d and xe2x80x9ccontainerxe2x80x9d are herein used interchangeably and the term module is loosely defined to mean a canister having an inner container and an outer container of the type described in the above referenced patent. The disposable canister in the referenced patent has an inner container and an outer container and is also described herein as a module. The outer container serves as the traditional disposal container typically made of steel, which is insulated from an inner container, typically of made of graphite, by a layer of insulating material. The inner container is usually lined in alumina and serves as a crucible to melt a waste, contain the waste in its molten state, and serve as the disposal container for the vitrified product.
In the referenced patent, waste is added to the inner container then heated until it is melted. The term xe2x80x9cmeltedxe2x80x9d is defined loosely herein consistent with the meaning understood by those skilled in the art. The term xe2x80x9cmeltedxe2x80x9d includes a molten waste containing unmelted components, such as refractories, within the molten waste. These refractories melt at temperatures well above normal vitrification temperatures, which can range from between about 900 to about 1600 degrees centigrade. The unmelted refractories are typically contained in the glassy matrix forming the vitrified product.
In the referenced patent, after the waste is melted, it is allowed to cool into a solid vitrified product.
Some drawbacks in using the method of the referenced patent included low fill volume, product inhomogeneity leading to nonuniform leaching responses at various elevations of the vitrified product, product crystallization, cesium volatilization, surface foaming; and corrosion of the alumina liner. The present invention addresses these drawbacks.
Accordingly, this invention is a process for melting waste in a disposable container to a level approaching 100% of the available volume, producing a homogeneous product which promotes a uniform leaching response, minimizing product crystallization, minimizing cesium volatilization, minimizing surface foaming inside the canister, and minimizing corrosion of the alumina liner. In addition, the invention will also shorten canister fill time and reduce heating power requirements.
The AVS Melting Process is a process for vitrification of waste in a disposable canister. In the process, waste is dropped into the disposable canister from the top. While the waste is being dropped into the disposable canister, radiant energy is added to the space above the waste in the canister, such that the temperature of the gaseous atmosphere above the waste is higher than the melting point of the waste. Since only the space above the waste in the canister is heated, the temperature of the melt decreases with increasing depth of the waste in the canister. The decreasing temperature permits a small surface melt volume to be maintained and solidified product to form with increasing depth. The process continues until the disposable canister is filled, then all heating is stopped and the disposable canister allowed to cool to ambient temperature.
The drawing illustrates the AVS Melting Process in a vertical cut-away of a canister. The gaseous atmosphere in the empty canister is heated to a temperature above melting point temperature of the waste such that a vitrified product can be formed. Then, waste, in the form of a dried particulates which may be heated to an initial temperature below the melting point of the waste, is added to the canister so that it creates a melt pool at the bottom of the canister. Then, only the gaseous atmosphere above the melted waste is heated to a temperature above the melting point of the waste such that as more waste is added, a solidified waste can form below the melt pool. When the canister is filled to the desired height with waste, the addition of waste and the heating of the gaseous atmosphere stops, and the canister is allowed to cool.